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MPEG-4

MPEG-4

The built-in settings included in the Prepare for HTTP Live Streaming destination and the built-in AAC setting (for audio output) use the MPEG-4 transcoding format, which encodes files using an H.264 encoder. This format encodes files for HTTP live streaming and for AAC audio files used in audio podcasting and digital music playback. To learn more about HTTP Live Streaming, see the HTTP Live Streaming Overview and other related documents available in the Mac Developer Library.

You can also create custom settings that use the MPEG-4 transcoding format.

The properties of built-in and custom settings that use the MPEG-4 transcoding format are listed below. The list includes properties in the General, Video, and Audio inspectors.

Important: When you add a setting (or a destination that includes settings) to a job, Compressor analyzes the source media and then automatically assigns the most appropriate setting properties (based on the setting’s transcoding format and the characteristics of your source media file). It’s recommended that you use the automatically assigned setting properties.

Setting summary

Displays the setting name and transcoding format, as well as an estimated output file size. When you add a setting to a job or change the setting’s properties, this summary automatically updates.

General properties

Name: Displays the name of the setting.

Description: Displays the description of the setting.

Extension: Displays the extension of the output file (.mp4 or .m4a).

Allow job segmenting: If you’ve set up distributed processing, select this checkbox to have Compressor process the output file using your shared computer group. For more information, see Transcode batches with multiple computers.

Note: Job segmenting is not available when outputting an MPEG-4 audio file or when the Multi-pass checkbox is selected in the Video inspector.

Default location: Choose an item from the pop-up menu to set the default save location for transcoded files.

Format: Use this pop-up menu to set whether the output includes video and audio, video only, or audio only.

Optimize for network use: Select this checkbox to create a file that will start playing after only a small portion of the file has been downloaded from the network.

Enhanced podcast: Select this checkbox to have Compressor embed podcasting information (annotations, markers, and artwork) into the output media file. For more information about annotations, see Add metadata. For more information about chapter markers, see Add markers.

Retiming

This section contains one property:

Set duration to: Sets the processing algorithm used to adjust the frame rate during transcoding. Select one of the following options:

[Percentage] of source: Modifies the output clip’s speed by a percentage of the source clip’s speed. Enter a value in the percentage field or choose a preset value from the adjacent pop-up menu (with a downward arrow).

[Total duration]: Sets the duration of the clip. Enter a timecode duration in the field or click the arrows to increase or decrease the time.

So source frames play at [frame rate] fps: Nondestructively changes the playback speed of the clip, without discarding frames or creating new frames. This setting has no effect unless the “Frame rate” value in the Video inspector is different than the source file’s frame rate. For example, if you add a 10-second source file with a frame rate of 24 fps to Compressor, set the “Frame rate” property in the Video inspector to 25 fps, then select “So source frames play at 25 fps” in the General inspector, the duration of the transcoded clip (at 25 fps) is 9 seconds and 15 frames.

Note: This option is not available when outputting an MPEG-4 audio file.

Frame size: Use the pop-up menu to set the frame size (resolution) for the output file.

Pixel aspect ratio: Use the pop-up menu to set the pixel aspect ratio (the ratio between the image frame width and height). You can also modify the aspect ratio of the output file using cropping and padding properties. For more information, see Modify frame size overview.

Frame rate: Use this pop-up menu to set the playback rate (the number of images displayed per second) for the output file. For more information, see Frame rate options overview.

Field order: Use the pop-up menu to set the output scanning method (either the field dominance or a conversion to progressive scanning). There are four options:

Same as Source: Maintains the same scanning method used by the source media file.

Top First: Scans interlaced fields, giving dominance (field order) to the top field, also known as field two, the upper field, or the odd field.

Bottom First: Scans interlaced fields, giving dominance (field order) to the bottom field, also known as field one, the lower field, or the even field.

H.264 profile: Use the pop-up menu to set the video compression for the output file. There are three options:

High: Provides high quality output.

Note: This setting is not compatible with older H.264 playback devices.

Main: Similar to the Baseline profile, with additional support for standard-definition (SD) video requirements.

Baseline: Primarily for video conferencing and mobile applications.

Entropy mode: Use the pop-up menu to set the entropy mode to CABAC, which provides higher-quality output, or CAVLC, which is faster.

Key frame interval: Enter a value in the text field to set the key frame interval (number of frames) at which you want key frames created in your output file. Alternatively, you can select Automatic to have Compressor choose the key frame interval rate (the displayed value is 0 with Automatic on; the actual value is determined during the encoding process).

Data rate: This pop-up menu allows you to choose a data rate for your video based on any of three options:

Custom: Enables a slider to set the number of kilobytes per second (kbps) to which you want to limit your video signal. Higher rates allow higher-quality video, but generate larger files that are slower to download or transmit.

Important: When you set a data rate, you override other codec-quality properties because the codec compresses the file as much as it needs to based on its data-rate limit.

Multi-pass: Select this checkbox to turn on multi-pass encoding that uses additional analysis of video frames to produce a high-quality output file. For faster (single-pass) transcoding, turn this feature off by deselecting the checkbox.

Customize the final cropping, sizing, and aspect ratio using the Cropping & Padding properties. Cropping removes video content from an image. Padding scales the image to a smaller size while retaining the output image’s frame size. For more information about these properties, see Modify frame size overview.

Cropping: This pop-up menu sets the dimension of the output image. The custom option allows you to enter your own image dimensions in the fields; other options use predetermined sizes. The Letterbox Area of Source option detects image edges and automatically enters crop values to match them. This is useful if you want to crop out the letterbox area (the black bars above and below a widescreen image) of a source media file.

Padding: This pop-up menu sets the scaling of the output image while retaining the output image’s frame size. The custom option allows you to enter your own scaling dimensions in the fields; other options use predetermined dimensions.

Quality

The following properties determine how the video will be resized, retimed, and otherwise adjusted when transcoded.

Resize filter: This pop-up menu sets the resizing method. There are three options:

Fast (Nearest Pixel): Provides the fastest processing time.

Better (Linear Filter): Provides a medium trade-off between processing time and output quality.

Best (Motion Compensated): Uses deinterlacing on areas of the source file that contain movement to produce high-quality output.

Reverse Telecine: Removes the extra fields added during the telecine process to convert the film’s 24 fps to NTSC’s 29.97 fps. Choosing this item disables all the other Quality controls. For more information, see About reverse telecine.

Adaptive details: Select this checkbox to use advanced image analysis to distinguish between noise and edge areas during output.

Anti-aliasing level: Sets the softness level in the output image. Double-click the value and then manually enter a new value or drag the slider to the right to increase softness. This property improves the quality of conversions when you’re scaling media up. For example, when transcoding SD video to HD, anti-aliasing smooths jagged edges that might appear in the image.

Details level: Sets the amount of detail in the output image. Double-click the value and then manually enter a new value or drag the slider to set the value. This sharpening control lets you add detail back to an image being enlarged. Unlike other sharpening operations, the “Details level” property distinguishes between noise and feature details, and generally doesn’t increase unwanted grain. Increasing this value may introduce jagged edges, however, which can be eliminated by increasing the “Anti-aliasing level” slider.

Video effects

For a list of available video effects and instructions on how to add a video effect to a setting, see Add and remove effects.

Sample rate: Use this pop-up menu to set the number of times per second that music waveforms (samples) are captured digitally. The higher the sample rate, the higher the audio quality and the larger the file size.

Data rate: Use the slider to set the number of kilobits per second (kbps) required to deliver your audio file. Using a higher rate will produce a higher-quality audio file.

Audio effects

For a list of available audio effects and instructions on how to add an audio effect to a setting, see Add and remove effects.